The present invention relates to lasers and, more particularly, to a method and apparatus for pumping a photolytic laser with a plasma pinch.
"Laser" is an acronym for light amplification by the stimulated emission, of radiation. In a laser, atoms, molecules, ions or crystals in excited states may be induced to emit radiation when stimulated by light of appropriate frequency. In a photolytic laser, intense beams of light dissociate molecules so as to establish a population inversion with respect to at least one photolysis product and initiate and sustain lasing activity. The process of creating excited states in the laser medium is termed "pumping".
One challenge in designing a photolytic laser is to provide effective pumping of the lasing medium. In other words, an efficiently generated intense pulse of radiation must impinge upon the particles of the photolytic lasing medium. Vacuum ultraviolet radiation provides one of the more useful wavelength ranges for laser pumping. However, due to the unavailability of suitable materials for transmitting vacuum ultraviolet radiation, it has proved difficult, if not impossible, to pump a laser by generating vacuum ultraviolet radiation outside a laser chamber and directing it into the chamber through a window.
It is known to generate vacuum ultraviolet radiation within the lasing chamber so that a window is not required. Hunter, Jr., U.S. Pat. No. 4,075,579 discloses an apparatus and method for the pumping of a laser by generating vacuum ultraviolet radiation throughout a lasing chamber. Noble gas atoms, excited by an electron beam, emit vacuum ultraviolet radiation to pump a photolytic lasing medium. There are at least two disadvantages to this approach. The first is the bulk of the electron beam generating apparatus. The second arises from the uniform excitation of the noble gas throughout the laser chamber. The uniform excitation results in excited noble gas atoms being in close proximity to the particles of the lasing medium and in particular to the excited photolysis products that are to support lasing activity. The excited noble gas molecules deactivate a percentage of the excited photolysis products through collisions quenching the population inversion without contributing to lasing activity.
It is also known to provide a more localized source of ultraviolet radiation by exploding wires. In this approach a large electric current explodes a wire extending across a laser chamber. A plasma, established by the explosion and located along the path defined by the wire, emits copious vacuum ultraviolet radiation which is used to pump a photolytic laser medium. The disadvantages of the exploding wire approach include: irregular vacuum ultraviolet emissions due to the uneven breakup of the wire, contamination of the chamber due to impurities in the wire, and the difficulty of replacing the wire rapidly enough for high repetition rate operation of the laser.
It is an object of the present invention to provide an improved apparatus and an improved method for the efficient pumping of a photolytic laser.